The present invention relates particularly to mineral fibre-containing elements that are produced by pressing and curing a mixture of mineral fibres and binder to produce a pressed board, often having a thickness of from 4 mm to 25 mm. These boards generally have a density of from 120 kg/m3 to 1000 kg/m3, such as 170 kg/m3 to 1000 kg/m3 and can be used as protective cladding on the outside of buildings or as acoustically insulating/absorbing ceiling or wall panels.
Previously, these products have been produced by subjecting a combination of mineral wool and binder to a mixing and forming process and subsequently pressing and curing the formed mixture to the desired density. The binder is generally either added to the mineral wool as dry binder, or uncured mineral wool is used where binder has been included during the fibre-forming and collection process.
Such products are technically and commercially successful, but we find that there is room for improvement. Specifically, we find that one problem with the methods of the prior art is that the mixing and forming processes used have a tendency to produce some compact balls of mineral wool in the mixture, or at least not to open up the compacted mineral wool. Furthermore, the methods used in the prior art do not contain any means for removing compacted mineral wool from the mixture so the uneven distribution is carried into the final product.
Where certain areas of the product have a higher density of mineral fibres, this can result in a higher concentration of binder in that area as well. Having an uneven distribution of mineral wool and binder in the product can be problematic for a number of reasons.
Firstly, there can be regions of the product where the binder is not cured thoroughly. This will decrease the overall strength and rigidity of the panel.
Secondly, where there is an uneven distribution of the components, this is likely to compromise the acoustic properties of an acoustic ceiling or wall panel.
Thirdly, as this type of panel is generally used in applications where the face of the panel is visible, it is important that the panels are aesthetically pleasing. An uneven distribution within the panel can result in undesirable inconsistencies at the surfaces. Where a high level of binder is concentrated in a small area, this can result in a spot on the surface of the product.
In some cases the surface of the panel will be painted and an uneven distribution of components or areas where the binder is not thoroughly cured can result in the paint not being accepted in an even manner across the surface.
Furthermore, in some products, especially those used as cladding for the outside of buildings, it has up to now been necessary to use a relatively high level of binder in order to provide a product of sufficient strength and rigidity. The high level of binder required is in part due to some binder being wasted as it is present in an unnecessarily high concentration in areas of the panel where there was compacted mineral wool in the mixture before pressing. As mentioned above, the full benefit of this binder is not transferred to the product, partly because it tends to be incompletely cured.
Having a high level of binder in the product is expensive and can reduce the fire resistant properties of the product. Therefore, it would be desirable to use less binder to provide a panel having a comparable strength and rigidity.
It is, therefore, an object of the invention to provide a method for forming a mineral fibre-containing element of the type described above having improved strength and rigidity or a reduced level of binder, or both.
A further object of the invention is to provide a method of forming a mineral fibre-containing element of the type described above that is homogeneous, having a more even distribution of components. It is also an object of the invention to provide a method for producing a mineral fibre-containing element having a surface with a more consistent and even appearance.
U.S. Pat. No. 2,682,085 discloses an apparatus for cleaning and opening fragile fibres, such as mineral wool fibres. This rather old prior art (filed 1949) suggests a relatively complex method and apparatus for opening and cleaning fibres to remove particles and dirt therefrom. Fibres are fed into the apparatus as bunches or masses of fibres. After opening and cleaning, fibres are collected in the form of a light, fluffy, low-density felted layer or web.
The aim of U.S. Pat. No. 2,682,085 is to clean and open the fibres for the formation of a light, fluffy, low-density web. The formation of rigid panels is not discussed in this document and no indication is given of the advantages of disentangling fibres and suspending them in an air flow in the context of the strength, rigidity, or any other property of a pressed and cured panel of the type used as cladding for buildings or as ceiling or wall panels.